Abstract: A method of sealing an electrical cable (2) into a wall (1) utilises a cable entry gland (3) having axially extending sleeves (3a), and the cable gland (3) is sealed to the cable (2) by means of shrink-down sleeving (9) extending over the sleeve portions (3a) and the surface of the cable (2). The cable gland is sealed into an aperture in the wall (1) by means of two "O" ring seals (5, 6) located on opposite sides of the wall (1) between a radial collar of the cable gland (3) and a clamping member (4). A test port (10) is coupled to the space between the portions of sleeving (9) and the "O" ring seals (5, 6) by fluid passages (8, 7) enabling testing of the integrity of the seal, for example by means of a device according to U.S. Pat. No. 2,145,233.

Abstract: Apparatus for providing a source of fluid pressure comprises a suction pump in the form of a spring-loaded bellows. The pump includes structure for registering a deviation of the bellows from a position of equilibrium, when coupled to a union, in response to leakage of a seal under test.

Abstract: A signal transmission device capable, for example, of use as a hybrid circuit in a voice frequency telephone transmission system, comprises a controllable substantially load independent current source shunting a signal path between input and output ports of the device. The shunt path is de-coupled from a signal source or load to be connected to respective ports of the transmission device by series connected impedances which are high in relation to those of the respective source or load, while the current source is arranged to respond to a voltage signal applied to the input port in order to drive corresponding currents through the impedances. A current steering circuit is provided to determine the relative magnitudes of the currents driven through the respective impedances, and thus to determine the virtual impedances presented to the signal source and load as well as the signal gain of the device.

Abstract: A method of forming and testing a fluid tight seal comprises placing a sealing ring between two members between which the seal is to be formed, either the sealing ring or the respective members being so shaped and arranged that lines of contact are formed between the sealing ring and the respective members between which there are continuous grooves or channels between the sealing ring and the respective member. By establishing a pressure difference between the continuous channels and the ambient atmosphere, the integrity of the seal can be tested by monitoring any fluid flow to or from the closed groove or channel. A single source of fluid pressure may be coupled to both grooves or channels via a union in one of the members and one or more transverse bores in the sealing ring.